Circuit arrangement for producing a high-frequency oscillation



June 19, 1951 E. H. HUGENHOL ,5

- CIRCUIT-ARRANGEMENT FOR PR UCING A HIGH-FREQUENCY OSCILLATION FiledOct. 19, 1948 INVENTO R 7 I Ed ucnd He TmanHu enho Patented June 19,1951 CIRCUIT ARRANGEMENT FOR PRODUCING A HIGH-FREQUENCY OSCILLATIONEduard Herman Hugenholtz, Eindhoven, Netherlands, assignor to HartfordNational Bank and Trust Company, Hartford, Conn., as trustee ApplicationOctober 19, 1948, Serial No. 55,262 In the Netherlands October 24, 19476 Claims.

This invention relates to circuit-arrangements for producing ahigh-frequency oscillation, of which the frequency is variable inaccordance with a control voltage supplied to the control grid of aregeneratively back-coupled discharge tube. It has more particularly forits purpose to provide a very simple circuit-arrangement forfrequencymodulation or after-adjustment of the frequency of ahigh-frequency oscillation.

In a known circuit-arrangement of this type, in which only one dischargetube is used, the oathode-circuit of this regeneratively back-coupledtube comprises a resistance, a reactance being provided between cathodeand grid. Due to this the phase displacement conferred on thehigh-frequency alternating voltage supplied to the grid of the tubedepends upon the high frequency voltage across the cathode resistance.Since a modulating control voltage influencing the mutual conductance ofthe discharge tube is at the same time supplied to the said grid, sothat the high-frequency voltage across the cathode-resistance is varied,the variable phase shift thus produced will cause a variation of thefrequency produced by means of the circuit-arrangement.

However, this circuit-arrangement suiiers from the disadvantage that,since the efiective mutual conductance of the discharge tube is notaltered by a variation of the grid bias, the value of a high-frequencyvoltage across the cathode resistance depends only to a small degreeupon the value of the modulating control voltage, so that theoscillation produced is variable in frequency to a low degree only. Thisdisadvantage might be avoided, for instance by making the modulatingcontrol voltage operative in the anode-circuit of the discharge tube. Inthis event, however, the required control voltage should be much higherand in addition the source of control voltage must supply anode currentfor the discharge tube, which entails a complicated circuit-arrangement.

The invention provides a different arrangement which permits by simplemeans a high-frequency oscillation to be produced of which the frequencyis variable with the aid of a regulating voltage supplied to the grid ofthe discharge tube. It has the advantages that the said control iseffected substantially without loss of energy and that considerablefrequency variations are possible. In one form of thecircuit-arrangement according to the invention the additional advantageis obtained that the amplitude of the alternating voltage supplied tothe grid of the discharge tube remains substantially constant, whichpermits the mutual conductance to be greatly varied.

According to the invention the feedback circuit of the discharge tubecomprises a voltage discriminative impedance of which the value variesin accordance with the amplitude of the alternating voltage generated inthe anode circuit of the discharge tube, as a result of which aphase-shift of the high-frequency alternating voltage is produced acrossthis impedance, which shift involves a frequency variation of theoscillation produced.

In order that the invention may be clearly understood and readilycarried into effect it will now be explained more fully with referenceto the accompanying drawing given by way of example.

In the drawing the reference numeral I denotes a discharge tube which isregeneratively fed back by way of the tuned circuit 2 and coupledinductance 3 with the result that a high-frequency oscillation isproduced, of which the frequency corresponds approximately to thenatural resonance of the tuned oscillating circuit 2 if the networkinserted in the said anode circuit of tube l and comprising a smallcondenser 4 and a voltage discriminative impedance, for example a biaseddiode 5, would not produce a phase-shift of the oscillation supplied tothe circuit 2. If the amplitude of the voltage produced in the anodecircuit is small so that the diode 5 does not carry current, this willbe the case since a small condenser 6 is connected in parallel with thediode 5. A modulating voltage is at the same time supplied, by way ofthe terminals 1, to the grid of the discharge tube I. The high-frequencyvoltage produced in the anode circuit of the discharge tube I willincrease with an increase in modulating voltage, owing to which thediode 5 carries current.

' In this event this diode 5 constitutes a resistance in parallel withthe condenser 6 with the result that the voltage fed to the circuit 2 isshifted in phase. Due to this the frequency of the oscillation producedWill adjust itself to a difierent value, since the total phasedisplacement of the high-frequency voltage between grid and anode mustbe 180. The choke coils 8 and 9 permit the passage of direct current andhave a high impedance to highrequency currents. The embodiment describedoffers the additional advantage that the amplitude of the voltageproduced across the oscillating circuit 2, and consequently also theamplitude of the alternating grid voltage of the discharge tube Iacquires a constant value, thus avoiding the disadvantage that byvarying the grid-adjustment of the discharge tube I With the aid of themodulating voltage I such a variable alternating anode voltage isproduced that the efiective mutual conductance of this tube shouldremain substantially the same.

The diode 5 may be replaced by a different voltage discriminativeimpedance, for example a rectifying cell. Furthermore, this impedanceneed not be inserted in the anode circuit of the discharge tube I butmay, in general, be inserted at an arbitrary point in thecircuit-arrangement by which it brings about a phase shift of thehighfrequency voltage, which depends upon the modulating voltage,

What I claim is:

1. Apparatus for producing high-frequency oscillations whose frequencyvaries in accordance with the instantaneous amplitude of a controlvoltage comprising an electron discharge tube provided with a cathode, agrid and an anode, a resonant circuit coupled between said anode andsaid cathode, a feedback circuit regeneratively coupling said resonantcircuit to said grid to sustain high-frequency oscillations in saidresonant circuit, a phase-shifting network interposed between said anodeand said resonant circuit and including an impedance element whose valuedepends on the amplitude of oscillations imposed on said network, thevalue of said impedance element determining the extent of phase-shaftimparted by said network, and means to apply said control voltage tosaid grid thereby to vary the amplitude of oscillations imposed on saidnetwork, whereby the frequency of said oscillations is varied inaccordance with the instantaneous amplitude of said control voltage.

2. Apparatus, as set forth in claim 1, wherein said impedance element isconstituted by a rectifying device.

3. Apparatus for producing high-frequency oscillations whose frequencyvaries in accordance with the instantaneous amplitude of a controlvoltage comprising an electron discharge tube provided with a cathode, agrid and an anode, a resonant circuit coupled between said anode andsaid cathode, inductive means regeneratively coupling said resonantcircuit to said grid to sustain high-frequency oscillations in saidresonant circuit, means to apply the control voltage to said grid tovary the amplitude of said oscillations, and a phase-shifting networkinterposed between said anode and said resonant circuit and including animpedance element whose value determines the characteristics of saidnetwork and depends on the amplitude of oscillations applied thereto.

4. An arrangement, as set forth in claim 3, wherein said network isconstituted by a capacitor coupled between said anode and one end ofsaid resonant circuit and a diode having an anode coupled to said oneend of said resonant circuit and a cathode coupled to the other endthereof.

5. An arrangement, as set forth in claim 4, further including a biassource whose negative terminal is connected to the anode of said diodeand whose positive terminal is connected to the cathode of said diode.

6. An arrangement, as set forth in claim 5, further including a radiofrequency choke interposed between the anode of said diode and saidnegative terminal.

EDUARD HERMAN HUGENHOLTZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,250,526 Frank et al July 29,1941 2,305,262 Lange Dec. 15, 1942 2,321,354 Bell et al June 8, 19432,361,731 Boch Oct. 31, 1944 2,378,245 Rath June 12, 1945

